Shaft assemblies such as motors and speed reducers generally include a housing in which a shaft is rotatably disposed. Motors generally include means for rotationally driving the shaft, which extends out of the housing through a bore. Speed reducers generally include a driven input shaft that rotationally drives one or more output shafts through gearing that controls the rotational speed of the output shaft(s). The input and output shafts extend into and out of the housing through respective bores. Shaft assemblies such as motors and speed reducers sometimes have a double output shaft.
Such assemblies often include a lip seal at the housing bore that extends between the housing and the shaft. The lip seal typically includes a rigid outer portion secured within the bore by an interference fit between the seal's outer circumferential surface and the bore's inner circumference. An elastomeric portion extends inward from the rigid outer portion to engage the shaft. This elastomeric lip bends axially inward toward the shaft assembly's interior, thus preventing the escape of lubricant from the interior area while providing an effective seal that prevents entrance of exterior contaminants into the interior area.